Various forms of encapsulating materials in glass articles have been known in the past, such as shown by the ornamental glass bottle of U.S. Pat. No. 502,461, the wired glass ribbon of U.S. Pat. No. 3,305,335, and the heat transfer cooking insert of U.S. Pat. No. 3,410,989. In addition to the full encapsulation of materials in glass articles as shown in the aforementioned patents, it is also known to seal or secure articles in molten glass during forming, such as shown in U.S. Pat. Nos. 314,828 and 2,219,573, and as suggested on page 22 of THE GLASS INDUSTRY, April 1978.
In U.S. Pat. No. 314,828, a charge of molten glass is deposited in a mold and a plunger carrying a metallic shank descends into the molten glass for the purpose of pressing the molten glass into the shape of a glass knob and embedding one end of the shank therewithin. U.S. Pat. No. 2,219,573, on the other hand, discloses the formation of a glass panel having an integral metal frame by positioning the frame within a mold and pressing a gob of molten glass into contact therewith so as to embed an inner peripheral flange of such frame within the glass panel. Such patent also discloses the positionment of pins within a mold assembly so as to press form a gob thereabout and integrally seal the pins in the thus formed glass body. THE GLASS INDUSTRY article entitled "The Mechanical and Chemical Aspect of Glass Sealing--Part II" by Marcus T. Borom (pp. 19-26) indicates on page 22 that from a manufacturing standpoint it is possible to form a ceramic-to-metal seal by embedding metal hardware in a mold, casting glass about it, and transforming the part to a glass-ceramic.
As can be seen from the foregoing prior art, not only did a variety of reasons exist for the desirability of encapsulating or sealing different materials within glass articles, but also a variety of materials which could be encapsulated were suggested including metal, silicon and graphite. However, although the prior art references are concerned with the encapsulation of materials within molten glass, none of the references except U.S. Pat. No. 2,219,573 and THE GLASS INDUSTRY article concerns itself with the differential expansion between the insert and the glass. The patent merely indicates that the metal insert should preferably have the same or similar coefficient of expansion as the glass to which it is to be bonded, whereas the article sets forth the complexity that is involved when encapsulating a metal within a glass having one coefficient of expansion which is then converted into a glass-ceramic having another coefficient of expansion. The article sets forth the desired end result of having the thermal properties of the insert material match that of the glass-ceramic to obtain a balanced seal in a bonded structure, but does not indicate a practical way of obtaining such end result or discuss the problems involved when the insert is not bonded to the glass or glass-ceramic material.
It thus has been an object of the present invention to set forth critical parameters which must be considered during the encapsulation of materials within glass and glass-ceramic articles and to set forth a method of encapsulating inserts within molten glass articles which are subsequently converted into glass-ceramic articles.